WASHINGTON — From the obscure perch of a backbench senator’s office, Katy Talento used to warn against what she saw as the health hazards of birth control pills — cancer, infertility and miscarriage. From his post at a Christian legal advocacy group, Matthew Bowman spent years attacking the requirement that most health insurance plans cover contraception under the Affordable Care Act.

Now on the inside — one at the White House, the other at the Department of Health and Human Services — Ms. Talento and Mr. Bowman have a clear path to prosecute their strong belief that birth control coverage should not be a mandate from Washington. Both are using arguments they honed over years of battle to ensure that a new rule, expected to be issued this month, to roll back the requirement can withstand legal challenge.

For some of the Trump administration officials tasked with reversing President Barack Obama’s legacy, the path forward has been somewhat rocky. Turning an ideological viewpoint into legislative or administrative policy able to pass legal muster can be difficult for Washington newcomers.

But the architects of the Trump contraceptive reversal, Ms. Talento, a White House domestic policy aide, and Mr. Bowman, a top lawyer at the Department of Health and Human Services, have the experience and know-how that others in the administration lack. As a lawyer at the Alliance Defending Freedom, Mr. Bowman assailed the contraceptive coverage mandate on behalf of colleges, universities and nonprofit groups that had religious objections to the rule. Ms. Talento, a former aide to Senator Thom Tillis, Republican of North Carolina, spent years warning about the health risks of certain contraceptives, especially birth control pills.

Ms. Talento, a Harvard-trained epidemiologist, mused two years ago on talk radio that she understood why doctors prescribed cancer chemotherapy drugs, despite their horrible side effects: The disease is worse. But why, she asked, would they prescribe the birth control pill?

“Pregnancy is not a disease,” she said. “Pregnancy is a sign of health.”

“There are other ways to avoid pregnancy and to space children’s birth if necessary and appropriate, if a family or a woman wants to do that,” Ms. Talento said. “You don’t have to ingest a bunch of carcinogens in order to plan your family.”

“The longer you stay on the pill, the more likely you are to ruin your uterus for baby-hosting,” Ms. Talento wrote in The Federalist, a conservative web magazine, before she became President Trump’s special assistant for health policy.

According to the National Cancer Institute, some oral contraceptives can lower the risk of endometrial and ovarian cancer and may contribute to a slight increase in the risks of breast, cervical and liver cancer. Some of the data came from older studies of the pill that had formulations and dosages different from what is commonly used now.

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President Barack Obama in 2012, with Kathleen Sebelius, the secretary of Health and Human Services.CreditStephen Crowley/The New York Times

In theory, the contraceptive coverage mandate removed cost as a barrier to birth control, a longtime goal of advocates for women’s rights and experts on women’s health. But to critics like Mr. Bowman and Ms. Talento, the rule was an egregious example of federal overreach. The new policy could take effect soon after it is issued in coming weeks.

The Affordable Care Act says insurers must cover certain preventive services at no cost. But the Trump administration says the law does not explicitly require coverage of contraceptives — an argument Mr. Bowman made for plaintiffs in court cases.

In the last five years, Mr. Bowman was involved in numerous court cases in which religious organizations and employers challenged the contraceptive coverage rule, which he calls an “abortion pill mandate.”

To justify a sweeping revision of the birth control rule, he and Ms. Talento invoke many of the same arguments and cite many of the same studies they have used in the past.

In blog posts and legal briefs that Mr. Bowman wrote as a lawyer at the Alliance Defending Freedom, he advanced arguments similar to those being used by the Trump administration to support the new draft rule. In a 2013 brief, he argued that the mandate was not justified by any “compelling governmental interest.”

The new draft rule, which he helped write, contends, “The government does not have a compelling interest in applying the mandate to entities with religious and moral objections.”

Women’s groups opposed to the new policy have threatened to sue, but the Trump administration will be ready. With arguments Mr. Bowman sharpened in the private sector, the administration has prepared a detailed legal justification to convince courts that the rule is not arbitrary or capricious.

Mr. Bowman successfully represented Conestoga Wood Specialties, a for-profit Pennsylvania company, and its Mennonite owners, who objected on religious grounds to providing coverage to employees for certain types of contraceptives. The Supreme Court in 2014 found in favor of Conestoga and, in a companion case, Hobby Lobby, a for-profit chain of craft stores.

“The government has provided no evidence that the mandate will reduce the number of unintended pregnancies,” said a brief filed for Conestoga by Mr. Bowman and his colleagues at the Alliance Defending Freedom, and they cited the experience of 28 states with similar requirements.

The new draft rule echoes the point: “In 28 states where contraceptive coverage mandates have been imposed statewide, those mandates have not necessarily lowered rates of unintended pregnancy.”

Further, Mr. Bowman wrote in a blog post in 2013, “if any connection exists between unintended pregnancy and bad health consequences, it is based on mere correlation, not causation.” The draft rule, echoing that argument, denies any “causal link.”

Ms. Talento and Mr. Bowman declined to discuss their prior work. But Douglas G. NeJaime, a professor at Yale Law School and a critic of the new policy, said, “We see something being achieved politically that was pushed in litigation for some time: a very broad exemption for certain employers without a mechanism to protect their female employees.”

Mr. Bowman was a law clerk for Judge Samuel A. Alito Jr. at the United States Court of Appeals for the Third Circuit, based in Philadelphia, just before the judge was appointed to the Supreme Court in 2006. Justice Alito wrote the majority opinion for the Supreme Court in the Hobby Lobby and Conestoga Wood cases.

Mr. Bowman also represented numerous Christian schools that challenged the contraceptive coverage mandate. They include Geneva College in western Pennsylvania, Oklahoma Baptist University, Southern Nazarene University in Oklahoma and Ave Maria School of Law in Florida, from which he received his law degree.

In similar cases, he also represented March for Life, a nonprofit that holds an annual march opposing abortion; Tyndale House, a religious publishing company; and James C. Dobson, the evangelical Christian whose radio broadcasts reach millions of Americans.

“Pro-life organizations must be free to operate according to the beliefs they espouse,” Mr. Bowman said when he filed suit for March for Life in 2014. “If the government can punish organizations simply because they want to abide by their beliefs, there is no limit to what other freedoms it can take away.”

Mr. Trump directed officials to rewrite the birth control mandate in an executive order “promoting free speech and religious liberty.” Ms. Talento said the order was part of the president’s “pro-life agenda.”

Dr. Eve Espey, the chairwoman of the department of obstetrics and gynecology at the University of New Mexico School of Medicine, who reviewed two of Ms. Talento’s essays at the request of The New York Times, said, “Multiple claims in these articles are not backed by science.”

“There is no evidence that hormonal contraception causes miscarriage,” Dr. Espey said, and “there is no evidence that hormonal contraceptives cause infertility.’’

Hormonal contraceptives carry more risk than pregnancy in only a very few situations, Dr. Espey said. In general, she said, the “regular use of contraceptives is a major contributor to health and to a reduction in pregnancy-associated mortality.”